Combined slaker-causticizer apparatus



July 13, 1965 s. M. NEUVILLE 3,194,638

COMBINED sLAxER-CAUSTICIZER APPARATUS Filed Nov. 21. 1962 2 Sheets-Sheet 1 July 13, 1965 s. M. NEUVILLE COMBINED SLAKER-CAUSTICIZER APPARATUS 2 Sheets-Sheet 2 Filed NOV. 2l. 1962 Flc. 2

United States Patent O @$4,638 COMBINED SLAKER-CAUSTHCZER APPARATUS Stewart M. Neuville, Harrison, Wis., assigner to Kimnearly-Clark Corporation, Neenah, Wis., a corporation oi' Delaware Filed Nov. Z1, i962, Ser. No. 239,118 2 Claims. (Cl. 2.3-2S3) This applicationv relates to an improved method and apparatus for the preparation of cooking liquor in the alkaline pulping of cellulosic materials. More specically it relates to a combined lime slaker and causticizer and an improved more ecient method for preparing white liquor for use in. alkaline pulping.

Economic operating of the alkaline pulping process requires the recovery and reuse of the chemicals employed in cooking the cellulosic source material. The rst step in recovering these compounds is to lirst concentrate and then burn the spent cooking liquor. The smelt obtained isthen dissolved to form what is known as green liquor. In the soda process, the Vgreen liquor is essentially a solution of sodiumA carbonate, while in the sulfate process, the green liquor also contains sodium sulphide. The next step in recovery is to causticize the green liquor by the addition of quicklime (CaO) to thereby convert the sodium carbonate to sodium hydroxide and produce white liquor suitable for reuse in the cooking process.

In conventional operations, slaking of the lime and subsequent causticization of the green liquor is done in separate units, each specially designed to carry out a ingle step of the process. Thus, strong green liquor is fed to a lime slaker-classier unit where it is mixed with and slakes a measured liow of quicklime. The resultant milk of lime ows to a classier sectionv for removal of coarse grit and unreacted material by means of a conveyor or rake-like device moving up the inclined bottom of the classifier tank. The degritted slurry overows from the claker-classiiier into a level-controlled headbox and is pumped from there through a series of tanks in which it is agitated, and the causticizing reaction, already started in the slarker, is completed. The causticized slurry then passes to a clarifier where the precipitated lime mud is separated out and is usually pumped to a thickener for recovery. The strong white liquor removed from the clariiier is then ready for use in cooking.

A serious disadavantage of the conventional slakingcausticizing system is the tendency for portions of the reacting slurry to overflow from one stage to the next without being retained in a particular reaction zone for the full time intended. This short-circuiting or bypassing of relatively unreacted chemicals is relatively ineicient and does not utilize the available chemicals to the best advantage. l

It is an object of this invention to combine the slaking and causticizing operation in a single unit thus providing savings in both equipment and space requirements.

A further obiect is to provide an improved and more efficient method for carrying out the slaking-causticizing operation, utilizing the improved apparatus to insure against short-circuiting or bypassing of relatively unreacted chemicals.

. Additional objects and advantages of the invention will become apparent from the following detailed description of certain preferred embodiments together with the accompanying drawing.

In the drawings, e

FIG. 1 is a sectional elevational one embodiment of a combined slaker-causticizer constructed in accordance with this invention and employed in carrying out the improved process.

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FIG. 2 is a perspective view showing in more detail the vertical and horizontal baffle structure in the apparatus.

FIG. 3 is a perspective view showing the details of a preferred structure for the agitator mechanism in the apparatus.

FIG. 4 is a perspective View showing in more detail annular seal plates comprising a part of the apparatus structure.

In accordance with the invention, the primary object is attained by arranging slaking and causticizing units in a single vertical tower. As shown in the drawings, a preferred embodiment of the combined slaker-causticizer tower comprises a closed vertical cylindrical vessel Ell divided into a top slaking compartment l2, and three causticizing compartments i3, 14 and l5, by hat horizontal floor elements in the form of annular stator baliles le, 17 and 1S suitable supported and mounted therein and provided with annular seal plates 23 extending to the interior lining 48 of vessel 1l.. These annular baffles are imperforate except for large central circular apertures l5", 2t? and 2l. Aperture i9 in baiie le, which separates slaking compartment i2 from the first causticizing compartment i3, is preferably flanged upwardly as at Z2 to provide baille 16 with an annular vertical portion. Apertures 26 and 2l do not have such auxiliary central flange. The annular baffles are rigidiiied and partially supported by vertical baies 5d extending through each compartment for the full height of the vessel and spaced at intervals. The vertical batiles Sti are normally spaced from the interior lining 48 of the vessel to avoid dead areas. it is also understood that more vertical bailies than the number shown in the drawing may be provided.

Top plate 2d of vessel l1 is provided with a diametrically extending mounting plate 25 carrying an electric motor 26 coupled to a central vertical shaft 27 extending vertically and axially of vessel 1l. Shaft 27 is rotatably mounted in bearing 28 on the floor of the vessel, and is provided with a seal 32 where it enters the tower. Shaft Z7 has fixed thereon a plurality of rotor bailes in the form of fiat, circular impertorate discs 29, Sti, Eil and agitators 33, 34, 35, and 36. Rotor baiiie 29 and agitator 33 are shown in this embodiment to be of unitary construction, while the remaining agitators and rotor battles are in spaced arrangement. Bale Z9 and agitator 33 may also oe in spaced arrangement, if desired. The rotor batiies are suitably sapced from their respective stator bailies to restrict the passage therethrough of iiuid being treated to prevent intermixing or short circuiting between compartments. A typical annular spacing is about l", but it may be varied to suit particular conditions. Top plate 24 is provided with a lime feed aperture 37 and an inlet pipe 38 for green liquor. The top plate also is equipped with a vent 39 andan access manhole di). Cylinder wall 41 in kslaking compartment l2 is provided with a flanged overow outlet 42 connected to the sewer or a suitable collecting vessel. A grit withdrawal outlet 43 is also provided in cylinder wall il near the base of slaking compartment l2. The cylinder wall in each of the causticizing compartments is provided with llanged discharge or cleanout outlets 4d, 45 and 46 near the base of each compartment with the latter outlet 46 also serving as the conduit for discharging fully causticized white liquor. An inspection manhole 47 may also be provided in the lowermost caustisizing compartment l5. Those parts of structure which come into contact with the chemical slurry are preferably made of stainless steel or other erosion or corrosion-resistant material. For example, the walls and bottom of cylinder 11 may be suitable lined with alkali-resistant brick 48, as shown, if the more expensive stainless steel is not employed for the cylinder wall structure.

In operation, strong green liquor is introduced through inlet 38, and a measured dow of quicktime, either reclaimed lime sludge or fresh lime, is introducedtbrough lime feed aperture 37, while rotor shaft 27, agitator 33 .and `rotor baille 29 are turned at a speed sullicient'to provide circulation and intimate intermixing of the chemical slurry to assist in the ini-tial slaking reaction while maintaining undissolved materia-ls inV uniform suspension. Rotor baille 29 is closely spaced from annular ilange or dam 22 of stator baflle 16 to restrict flow from the slaking compartment l2 into the rst causticizing compartment 13 thus preventing undesirable short-circuiting, The annular flange 22 further serves to retain in slaking compartment l2 large grit particles and unreacted material which settles outfor subsequent removal through grit withdrawal outlet 43 suitably equipped with a gate valve or the like. Centrifugal action of the agitator 33 and rotor baille 29 also tends to `direct the undesirable coarse particles of grits and unreacted material in the slurry to the periphery of stator baille 16 from where the particles are removed by continuously or intermittently withdrawing a portion of the slurry through outlet 43 by means or" a suitable exterior pump, not shown. The withdrawn portion of the liquor containing the grits is subsequently screened, the grits discarded, and 4the degritted liquor returned to the yslaking compartment. The degritted liquor may 'be returned through vent 39 thereby serving as a wash for fumes and dust being vented therethrough. The reacted liquor in the slaking compartment llows into the rst causticizing compartment through the -restricted annular .aperture formed by closely spaced rotor baille 29 and dam 22. Such spacing may be adjusted as desired, but a 'spacing of about 1" was found to work satisfactorily. The flow continues to each of the causticizing compartments in sequence through the restricted lannular apertures shown, and substantiallyk fully reacted and causticized white liquor is removed continuously through discharge conduit 46. After claricat-ion to remove lime mud, the clarified causticized liquor is ready for use in the pulping operation. Thelime mud removed in the clarifying step is washed, thickened and reburnt to convert it to CaO, for subsequent reuse in the slaking-causticizing operation.

The size of the vessel and each compartment is such that total retention time of the liquor is suillcient to obtain optimum reaction for each stage of the process. For example, about l minutes in the slaking compartment, and a total of about 2 hours in the causticizing section is suillcient to bring the reaction to substantial completeness. The causticizing section is compartmented and `connected by restricted openings as shown, to prevent short-circuiting between reaction zones, and insuresagainst intermixing of less reacted material with more completely reactedmaterial. The number and size of the individual causticizing compartments may be varied to suit particular conditions, depending on-total capaoity designed int-o equipment, rate of ilow, andthe like.

In startup operation, the vessel is first lilled with green liquor to operating level 49 before lime is introduced. A major portion of the green liquor used in initial filling is substantially unreacted and may be shunted back to the green liquor feed until acceptable ful-l strength white liquor is obtained at the discharge end.

While this specific example relates to reconstituting green liquor derived from spent alkaline cooking liquor, the process ,and apparatus is equally applicable to the preparation of fresh cooking liquor from unslaked lime and fresh sodium carbonate solution.

The chemical reaction involved in the slaking-causticizing operation is well known and proceeds in two stages. In the first, or slaking, stage, calcium oxide (CaO) lof the lime llrst reacts with the water in the green lliquorto form calcium hydroxide (Ca(OH)2) with thek evolution of considerable heat.l This reaction may be written as follows.

The resultant calcium hydroxide then reacts with the sodium carbonate in the green-liquor to form sodium hydroxide and calcium carbonate precipitate. This causticizing reaction may be written:l

Although written in two stages, the reactions actually overlap, and par-t of the causticizing -occurs almost simultaneously with the slaking. The reaction is reversible to some extent, and lall the sodium carbonate 4cannot be converted to sodium hydroxide no mater how much lime is used.- Howevenfthe use of hot fresh lime, high temperature, and intimate mixing tall aid in improving ellioiency. It is underst'oodVthat means may be provided for regulating temperature of the reaction at its optimum level.

The apparatus Iand method described in this invention make possible more complete mXIlg, better temperature control, a simpler Vllow pattern, all combining to produce a more uniform liquor than vwas hitherto possible and at substantial savings in cost.

When the slaking-causticizing operation is carried out in the apparatus shown and by the method described, several advantages result. The unitary construction is more economical, utilization of Vgravity llow requires less complicated and expensiveauxiliary equipment, and reten- -tion time is more easily controlled thus permitting more complete causticizing and `better overall efficiency.

It will be understood that various changes in fthe process details and arrangements of parts herein described and 4illustrated for the purpose of'explaining the invention may be made by those skilled in the art within the principles and scope of the invention las defined in the appended claim-s.

What is `claimed is: Y 1. A combined slaker-causticizer .apparatus comprising a vertical cylindricalvessel, a *pluralityy of spaced `stationary horizontal imperforate batlles dividing said vessel into superposed compartments, said baflles having central apertures therein for communication between said con1- par-tments, an upstanding iiange disposed around the circumference of :the central aperture in theV uppermost compartment, |a shaft rotatably mounted axially of said vessel and extending through said compartments, hor-izontal rotating imperforate batlles mounted on said shaft adjacent to and closely vspaced from each rof said apertures, agitating means located in each compartment and mounted on said shaft, means forgadrnitting both dry and liquid reaction chemicals into the uppermost of said cornpartments for mixture therein, outlet means near the door of said uppermost compartment and communicating with an exterior of the vessel for withdrawing from the uppermost compartment a portion of the reaction mixture containing coarse particles, and youtlet means at the base of the l'owermost compartment of said vessel-for removing fully reacted chemicals. Y

2. A combined slaker-causticizer apparatus comprising a vertical cylindrical vessel, a plurality of horizontal annular stator imperforate baffles :axially spaced in said vessel to divide said vessel into a plurality of superp-osed reaction chambers, said baflles having centrally disposed circular apertures therein dening communicationcha'nnels'between said chambers, an upwardly extending liange coextensive with the circularfa-perture in thefloor of the uppermost chamber, a plurality of annularly spaced stationary vertical baillesextending radially inward from the outer peripheryof said horizontal batlles, av rotatably mounted shaft extending axially of said vessel, a plurality of ilat horizontal circular rotor imperforate battles mounted on said shaft and closely spaced above each of said apertures to partially' Irestrict communication between said chambers, agitator means mounted on said shaft for rotation in each of said chambers, inlet means above the uppermost chamber for admitting a reactive uid `chemical therein, a second inlet means `above said uppermost chamber for admitting a reactive solid chemical therein, outlet means near the oor of said uppermost chamber and communicating with the exterior of the vessel for withdrawing a portion of the reaction mixture containing coarse particles from said chamber, and outlet mea-ns near the oor of the lowermost chamber for withdrawing fully reacted chemica-ls.

References Cited by the Examiner UNITED STATES PATENTS Zellweger 259-66 Moore et al. 23-133 Robinson et a1. 259-66 Knight 162-30 Walker 23-185 Samaniego et al. 259-108 10 MORRIS o. woLK, Primary Examiner.

WILLIAM B. KNIGHT, Examiner. 

1. A COMBINED SLAKER-CAUSTICIZER APPARATUS COMPRISING A VERTICAL CYLINDRICAL VESSEL, A PLURALITY OF SPACED STATIONARY HORIZONTAL IMPERFORATE BAFFLES DIVIDING SAID VESSEL INTO SUPERPOSED COMPARTMENTS, SAID BAFFLES HAVING CENTRAL APERTURES THEREIN FOR COMMUNICATION BETWEEN SAID COMPARTMENTS, AN UPSTANDING FLANGE DISPOSED AROUND THE CIRCUMFERENCE OF THE CENTRAL APERTURE IN THE UPPERMOST COMPARTMENT, A SHAFT ROTATABLY MOUNTED AXIALLY OF SAID VESSEL AND EXTENDING THROUGH SAID COMPARTMENTS, HORIZONTAL ROTATING IMPERFORATE BAFFLES MOUNTED ON SAID SHAFT ADJACENT TO AND CLOSELY SPACED FROM EACH OF SAID APERTURES, AGITATING MEANS LOCATED IN EACH COMPARTMENT AND 